A workpiece processing system may include, but not be limited to, plasma processing systems such as doping, etching, and deposition systems. A workpiece processing system may also include a beam-line doping system such as a beam-line ion implanter. As a workpiece in such systems is treated, outgassing may occur from the workpiece. Such outgassing can lead to unstable and/or non-repeatable conditions. Therefore, it is desirable to sense and control such outgassing.
For instance, two types of workpiece processing systems include plasma doping and beam-line ion implanters. In a plasma doping ion implanter, a source may generate plasma within a process chamber. A platen is positioned in the process chamber for supporting a workpiece, and ions may be accelerated from the plasma into the wafer. In a beam-line ion implanter, a desired impurity material is ionized in an ion source, the ions are accelerated to form an ion beam of prescribed energy, and the ion beam is directed at a front surface of the workpiece.
In both the plasma doping and beam-line ion implanters, it may be desirable to operate the ion implanter at a relatively high dose rate in order to increase throughput. However, operating at such relatively high dose rates can exacerbate outgassing from the workpiece, e.g., a semiconductor wafer or wafer in one instance. Outgassing from the wafer may occur when ions strike films or layers on the wafer such as a photoresist layer. A photoresist layer is used to mask selected areas of the wafer surface so ions are implanted only in the unmasked areas. During ion implantation, the energetic ions may break up chemical bonds within the photoresist layer. As a result, outgassing byproducts such as volatile organic chemicals and/or other particles may be released. This may be referred to generally in the art as “outgassing,” or “photoresist outgassing” when the outgassing is attributable to the photoresist layer.
High rates of outgassing from the wafer in ion implanters can lead to unstable and/or non-repeatable implant conditions. High rates of outgassing can also contribute to contamination in ion implanters as the energetic ions collide with the outgassing byproducts. In addition, in plasma doping ion implanters, outgassing byproducts can lead to arcing in the process chamber that can damage the devices being formed on the wafer. Therefore, it is desirable to sense a parameter representative of an outgassing rate. One conventional parameter that may be sensed in plasma doping ion implanters is global pressure in the process chamber sensed by a pressure sensor positioned relatively far away from the wafer. However, this pressure sensor has accuracy and time delay drawbacks.
Accordingly, there is a need to provide another technique for outgassing rate detection that overcomes the above-described inadequacies and shortcomings.